It is fascinating watching Google expand its sphere of influence into offline media. Their acquisition of dMarc Media Networks will add the ability to research, buy and manage radio campaigns to their online advertiser tools. Similar capabilities for television, outdoor, newspaper and magazine advertising will not be far away.

The move makes sense. Google's financial success is less about its technical search capability, and a lot to do with its innovation in commercialising it. By making it easy for advertisers to directly target their ads to related searches, Google solved the classic supply and demand inventory equation that dogs the entire marketing industry.

There are many similar problems in offline markets. Advertisers fight for prime positions (front of newspapers, popular TV series slots) and significant remnant inventory goes unsold or underpriced. The key to achieving better yields on that inventory is to be able to measure response. Who cares if your ad runs at 3.30pm in the afternoon if it sells 30% more of your product? And even if it sells less than a prime time slot, it may be more cost effective to buy twice for half as much.

There is a catch however. In search advertising, inventory scales with demand. The more searches that take place, the more slots that become available in real time for advertisers chasing eyeballs. Offline media, with set transmission times and publication deadlines has less flexibility and ultimately a finite amount of inventory available for commercialisation.

But it is not hard to imagine a time when most of our media goes to an on demand model, and inventory becomes a truly fluid resource. And if Google play their cards right, they will be there waiting for us.